The main goal of this project is understanding the role of virus encoded cell surface proteins in murine leukemia and their possible role in the maintenance of normal hematopoetic cell homeostasis. We have concentrated our recent efforts on developing monoclonal antibodies specific for viral polypeptides of distinct classes of MuLV. Certain mouse strains undergoing adult graft-versus-host response induced by parent arrow to the rightF1 adoptive transfer develop serum antibody to MuLV. We have developed a series of hybridomas from these mice which detect unique determinants of ecotropic, xenotropic and MCF MuLV envelope polypeptides. Of particular importance is a series of monoclonal antibodies reacting with group- or strain-specific xenotropic MuLV env determinants. The viral specificities of serum antibodies generated during GVHR was found to vary depending on the mouse strains used and the evidence suggests that antibody production may be influenced by endogenous proviral genes of the donor strain. We are currently using the monoclonal antibodies to define the strain and organ distribution of various MuLV env determinants in both high and low leukemia mouse strains.